Some people are complaining are making the claim that the dragon will curbstomp the party "if it is played at all intelligently." I think it's important to remember the skill level of a monster never exists in a vacuum. It is always relative to the skill level of the players. So maybe you don't play it with as much intelligence as you would against a team of seasoned optimizers. Just use tactics that make it seem smart compared to other fights that have occurred in your campaign.

CR is also relative. If an "appropriately CRed" dragon is too powerful for the party to face, than its CR isn't really appropriate. Look over the statblocks of weaker dragons and find one of lower CR that seems about right for the way your party fights. That way, you can trick your players into bunch together, punish them with a breath weapon that doesn't kill them, and watch them get scared and adjust on the fly. They'll feel like they fought somebody really tough even if the dragon supposedly isn't by some nonexistent objective standard.